1. Field of the Invention
The present invention relates generally to aircraft gas turbine engine variable stator vanes and, more particularly, seals deposed around trunnions of such vanes.
2. Disscussion of the Background Art
A typical gas turbine engine compressor includes several rows or stages of interdigitated compressor stator vanes and corresponding rows or stages of compressor rotor blades. As ambient air flows through each succeeding compressor stage during operation, it is successively compressed for providing compressed air to a combustor located downstream therefrom, wherein it is mixed with fuel and ignited for generating hot combustion gases which power the engine. One or more rows of compressor stator vanes are variable for allowing each vane to rotate around a longitudinal or radial axis to adjust the angular orientation of the vane relative to the airflow. This improves the efficiency and overall operation of the compressor. Variable stator vanes typically include an integral outer trunnion disposed in a stator casing for allowing angular adjustment of the vane relative to the airflow thereover. In a typical compressor, the trunnion is pivotally mounted in a bushing in the casing of the compressor or in a complementary mounting boss on the casing.
One problem with current designs is that compressor air leaks through air seals around the trunnion. Aerodynamic forces, acting on the vane, orients the vane into a cocked position opening up or increasing area of a leakage path. The leakage path allows compressed hot air to flow by the bushing degrading the bushing by oxidation of the resin system. One type of bushing material is a high temperature polyamide composite laminates. The high temperature air leak can exceed 700 degrees F in some applications and decompose the polyamide bushing materials causing severe bushing degradation due to erosion and oxidation of the resin matrix. This in turn leads to further degradation due to loss of the fiber because of fatigue failure. Manufacturing tolerances and maintenance practices are also known to causes larger leakage passages. Therefore, it is highly desirable to improve sealing effectiveness of variable vane assemblies having a trunnion and a bushing between the trunnion and the engine casing.